CN107709018B

CN107709018B - Multi-waveform inkjet nozzle correction

Info

Publication number: CN107709018B
Application number: CN201680038535.5A
Authority: CN
Inventors: 约翰·达菲尔德
Original assignee: Electronics for Imaging Inc
Current assignee: Electronics for Imaging Inc
Priority date: 2015-06-04
Filing date: 2016-06-03
Publication date: 2020-05-19
Anticipated expiration: 2036-06-03
Also published as: EP3302982A4; US9718269B2; ES2903158T3; EP3302982B1; EP3302982A1; WO2016197061A1; US20160355009A1; CN107709018A

Abstract

The uniformity of inkjet nozzle performance within a printhead containing a plurality of nozzles within the printhead is optimized by characterizing one or more performance attributes of the plurality of nozzles within the printhead. The generated waveform ensemble includes a plurality of waveforms to compensate for differences in one or more performance attributes in the plurality of nozzles. One of the waveforms within the waveform set is assigned to each nozzle to optimize one or more performance attributes of each nozzle relative to each other nozzle in the printhead. Each nozzle in the printhead responds substantially uniformly with respect to each other nozzle in the printhead based on the waveform assigned to each nozzle.

Description

Multi-waveform inkjet nozzle correction

Cross Reference to Related Applications

This application claims priority to U.S. patent application Ser. No. 14/731,367, filed on 4/6/2015, which is hereby incorporated by reference in its entirety.

Technical Field

The present invention relates to printing. More particularly, the present invention relates to multi-waveform inkjet nozzle correction.

Background

In the prior art, industrial print head designs use one identical waveform to drive all the nozzles in the print head. In such printheads, grayscale printing uses portions of the same waveform, which compromises performance and consistency. This approach can lead to common print defects such as drop volume variation, drop velocity differences, and print density defects.

Disclosure of Invention

Uniformity of performance of inkjet nozzles within a printhead containing a plurality of nozzles is optimized by characterizing one or more performance attributes of the nozzles in the printhead. The generated waveform ensemble includes a plurality of waveforms to compensate for differences in one or more performance attributes in the nozzles. One of the waveforms within the waveform set is assigned to each nozzle to optimize one or more performance attributes of each nozzle relative to each other nozzle in the printhead. Each nozzle in the printhead responds substantially uniformly with respect to each other nozzle in the printhead based on the waveform assigned to each nozzle.

Drawings

FIG. 1 is a graph of velocity data for one of two channels in a printhead provided by the manufacturer;

FIG. 2 is a graph showing a waveform map for each print nozzle for one of two channels in a printhead according to the present invention in view of velocity data provided by the manufacturer;

FIG. 3 is a graph illustrating color density analyzed by a nozzle according to the present invention;

FIG. 4 is a graph of waveforms distributed to a plurality of nozzles in accordance with the present invention;

FIG. 5 is a graph of a dithered waveform distribution according to the present invention;

FIG. 6 is a flow chart of a method for optimizing inkjet nozzle performance uniformity within a printhead containing a plurality of nozzles in accordance with the present invention;

FIG. 7 is a flow chart of a method for multi-waveform inkjet nozzle calibration according to another embodiment of the present invention;

FIG. 8 is a perspective view of a printer used in accordance with the present invention;

FIG. 9 is a perspective view of a printer carriage used in accordance with the present invention;

FIG. 10 is a perspective view of a printer printhead layout used in accordance with the present invention;

FIG. 11 is a perspective view of a printer printhead used in accordance with the present invention; and

fig. 12 is a schematic block diagram of a machine in the exemplary form of a computer system within which a set of instructions may be executed to cause the machine to perform one or more of the methodologies discussed herein.

Detailed Description

The uniformity of inkjet nozzle performance within a printhead containing a plurality of nozzles within the printhead is optimized by characterizing one or more performance attributes of the plurality of nozzles within the printhead. The generated waveform ensemble includes a plurality of waveforms to compensate for differences in one or more performance attributes in the nozzles. One of the waveforms within the waveform set is assigned to each nozzle to optimize one or more performance attributes of each nozzle relative to each other nozzle in the printhead. Each nozzle in the printhead responds substantially uniformly with respect to each other nozzle in the printhead based on the waveform assigned to each nozzle.

Some embodiments of the invention provide for differential correction of one or more performance attributes in nozzles by selecting different waveforms to drive individual nozzles in a printhead. First, based on the final test data of the printhead manufacturer, consider the concept of correcting differences in one or more performance attributes of the plurality of nozzles, which manifest themselves as specific defects. Modern industrial inkjet printheads typically have hundreds of nozzles per unit, some over 2000. The cost of these units ranges from about $ 1 per nozzle to up to $ 10 per nozzle. Less expensive printheads generally have more variances and deficiencies, and the presently preferred embodiments of the present invention are directed to such printheads in at least some embodiments.

Most printhead manufacturers generate final test data on each printhead, while some manufacturers provide this data on a per nozzle basis. These data include factor attributes such as nozzle speed, directionality, mechanical tolerances, etc. Embodiments of the present invention use some of this data to correct for more important differences in the printhead based on individual control of each nozzle. As shown in table 1 below, the velocity difference of the nozzles is an example of a defect corrected in this way.

TABLE 1 nozzle speed Difference

FIG. 1 is a graph of velocity data for one of two channels in a printhead provided by the manufacturer. The data shows that the nozzle velocity difference from nozzle #1 to nozzle #254 is 5.1m/s (+/-6%). By creating a particular set of waveforms, for example, seven different waveforms (see table 2 below), the waveform driving the slower nozzle can be applied to the nozzle that appears faster in the data, and vice versa, to offset the speed difference.

TABLE 2 specific waveform set

Speed m/s	Waveform #
		4.8	7
4.9	6
		5.0	5
5.1	4
		5.2	3
5.3	2
		5.4	1

Fig. 2 is a graph showing a waveform map of individual print nozzles for one of two channels in a printhead in view of velocity data provided by the manufacturer. Literally, it can be seen that the waveform map is a mirror image of the velocity data. A fast nozzle firing at a speed 6% above the average (i.e., 5.4m/s) will decelerate by 6% and fire at a speed of 5.1m/s driven by waveform 7. A slow nozzle firing at a speed of 6% below the average (i.e., 4.8m/s) will accelerate 6% and fire at a speed of 5.1m/s driven by waveform 1. Ideally, if this correction is applied, all nozzles will eject at 5.1m/s, appearing as a very uniform, more expensive printhead.

The manufacturer speed data is only one of the raw data that can be used in the present invention to correct for performance attribute differences (e.g., defects in the print head) by manipulating the waveform sent to each nozzle. This may not be the most effective way to correct for, for example, speed defects, because the manufacturer may generate such data on equipment that is not representative of the actual application of the printhead, e.g., static versus reciprocating, test liquid versus Ultraviolet (UV) curing ink, different emission frequencies, etc.

In the embodiment of the invention, the more accurate data generation method comprises the following steps:

a. printing a specific test pattern on the printer at the correct frequency (speed) using the correct ink and generating an image on the device in exactly the same way;

b. capturing a highly accurate digital image of the test pattern by a camera or scanner;

c. image analysis is applied to determine one or more performance attributes of the ink drops, i.e., size, shape, location, satellite performance, etc.

d. Such performance attributes are extracted to generate printer and printhead specific waveform maps to correct defects to provide more accurate suitability results than manufacturer data.

Using the above method, other defects not present in the raw data can also be captured and analyzed, and the waveform corrections disclosed herein can be applied. The defects may include, for example, general density shifts in the finished image.

Images are typically completed by interleaving multiple (e.g., four or more) print passes by offsetting random errors from each other when using less expensive print heads. However, in some faster printing modes, these fine defects of the print head can accumulate to form more significant defects that are visible to the naked eye.

When a general defect (e.g., a density shift of the same color) is detected, the image may be analyzed to determine the severity and magnitude of the defect. In a particular print mode, only one color channel is typically used to create and complete a particular test print job that is defect-enhanced. The completed test print job is then digitally captured using a high resolution camera or scanner. An analysis tool is applied to the captured image to quantify the defects. The output of the analysis tool is typically graphical and therefore easily corrected for density defects. Referring to fig. 3, the nozzle color density after analysis is shown.

If the defect is graphically indicated, a second tool is used to perform waveform correction on the print head. Embodiments of the present invention apply a step (step) difference to the waveform in its simplest form. Fig. 4 illustrates the waveform dispensed to the nozzle.

Although in most cases this complexity is sufficient to correct 80% of the density defects, some more severe defects require a higher correction margin. With large increments (> 1%) between waveforms, key images may show step transitions between each other, creating respective defects. To overcome these step defects, it is necessary to dither between the waveforms to mask the transitions between each other. Referring to fig. 5, a waveform distribution of jitter is shown. A tool for correcting the defect application waveform has a complexity that automatically dithers between waveform steps.

Operation of

FIG. 6 is a flow chart of a method for optimizing uniformity of inkjet nozzle performance within a printhead containing a plurality of such nozzles. In fig. 6, the nozzles on the printhead are optimized by characterizing one or more performance attributes of the nozzles within the printhead (90). The performance attributes include any of drop velocity, drop volume, drop mass, optical density produced by the printhead, gloss, and printhead temperature. In embodiments of the present invention, one or more performance attributes may be characterized using a printed test pattern that is subsequently imaged and analyzed.

A waveform ensemble (92) including a plurality of waveforms is generated to compensate for differences in one or more performance attributes in the plurality of nozzles. One of the plurality of waveforms within the waveform set is assigned to each nozzle (94) to optimize one or more performance attributes of each nozzle relative to each other nozzle in the printhead.

Each nozzle in the printhead responds substantially uniformly with respect to each other nozzle in the printhead based on the waveform assigned to each nozzle.

The waveform set comprises a discrete finite waveform set. One of a plurality of waveforms is assigned to each nozzle using a dithering operation. The dithering operation may also be used to smooth transitions between discrete waveforms.

In an embodiment of the present invention, the performance of a predetermined portion of a plurality of nozzles of a print head is taken as a reference. Adjusting the plurality of nozzles outside the predetermined portion by assigning a waveform to the outer plurality of nozzles to adjust the outer plurality of nozzles to approximate performance of the plurality of nozzles within the predetermined portion.

Embodiments of the present invention also include scanning printers in which the consistency of the performance attributes produced by a given color channel is improved by characterizing the combined average of the performance attributes of all print heads within the printer. The waveforms are selected from among the waveforms for each printhead nozzle to make the performance attributes of the plurality of printhead nozzles more consistent. The same selected waveform is applied to each printhead printing a given color channel. The performance attribute includes any of drop velocity, drop volume, drop mass, optical density produced by the printhead, gloss, and temperature of the printhead. In embodiments of the present invention, one or more performance attributes are characterized using a printed test pattern that is subsequently imaged and analyzed.

Alternative embodiments

FIG. 7 is a flow chart of a method for multi-waveform inkjet nozzle calibration according to another embodiment of the present invention. By selecting different waveforms, embodiments of the present invention provide for the correction of specific print defects to drive individual nozzles in a printhead. In some embodiments of the present invention, a characteristic curve is generated to eliminate print head defects, and the waveform values for each nozzle in the print head may be stored in a look-up table. In some embodiments of the invention, the dither pattern is then superimposed onto the curve to blend with the difference. In embodiments of the present invention, the portion of the curve that needs to respond continuously should be set as the reference waveform to maintain consistent color and performance. Other embodiments of the present invention use print head characterization data (i.e., individual nozzle velocity) to generate specific drive patterns to correct for dot placement errors due to differences. Embodiments of the present invention also limit adjacent jitter increments to, for example, 0.1-0.5 mus timely pulses to avoid step and crosstalk defects.

In fig. 7, a print command is received at the printer for the printer to perform a print job at two or more nozzles in a print head within the printer. Thereby, the printer prepares to perform a print job at the nozzle n (100). A waveform is selected (102) from a look-up table (104) and applied to nozzle n. In an embodiment of the invention, a dither pattern 106 is applied in which the waveform size at adjacent nozzles is checked (108) to determine if a limit is exceeded (110). If so, the waveform adjustment of the nozzle is limited (112); otherwise, the nozzle may print using the adjusted waveform (114). If the print job is complete (116), the process ends; otherwise, increment nozzle n, the process will repeat beginning with nozzle n + 1.

Embodiments of the present invention are implemented in connection with an industrial printhead for use in a high-speed digital UV inkjet printer such as Vutek HS 100. FIG. 8 is a perspective view of a printer used in accordance with the present invention; FIG. 9 is a perspective view of a printer carriage used in accordance with the present invention; FIG. 10 is a perspective view of a printer printhead layout used in accordance with the present invention; and FIG. 11 is a perspective view of a printer printhead used in accordance with the present invention.

Modern printers may have 50 or more printheads. Each print head costs $ 1000-2000. It is advantageous to use a lower cost print head to achieve the quality of a high cost print head. Embodiments of the present invention independently characterize each of the print head nozzles and create a library of look-up tables for the print head so that each nozzle has nearly the same performance as each of the other nozzles, although differences due to temperature, etc. may also exist. This allows lower quality and/or cheaper printheads to be used in the printer.

In embodiments of the present invention, each of the inkjet nozzles is driven by a different waveform, so that correction of a specific printhead defect can be achieved. The system drives each nozzle slightly harder or slightly softer to cause the droplets to come out relatively faster and larger or relatively slower and smaller. If the defect involves a slow nozzle or a fast nozzle, one or more of the nozzles may be accelerated or decelerated by imparting a different waveform to each nozzle to correct the defect.

Typically, the printhead manufacturer provides data on typical nozzle speeds. In embodiments of the invention, these velocities are varied by varying the width of the waveform pulses delivered to each nozzle, where at one point, wider pulses deliver more energy to accelerate the ink and narrower pulses deliver less energy to decelerate the ink. It will be appreciated that the pulse width may not be able to accelerate the ink at some point due to resonant and non-resonant effects. In addition, other methods may be used to vary the ink speed.

Recent developments have shown that certain defects are not caused by drop volume or velocity as characterized by test data. For example, differential heating of the printhead can result in slower ink drop firing speeds from the cooler nozzles. To correct this problem, a variable waveform is used to counteract and enhance the inert nozzle. Also, additional non-fire pulses may be applied to the inert nozzle regions of the printhead to conduct heat. Localized heating of the print head eliminates temperature differences, thereby achieving more consistent correspondence. Therefore, a key defect to correct is a temperature defect, where the temperature of the print head at the ends tends to be lower than the temperature of the middle portion. A nozzle with a lower temperature will tend to spray more weakly and more slowly. Embodiments of the present invention may drive the nozzle with increased force at the tip to correct for this defect. As described above, the waveforms used to drive the print head nozzles are typically square waves, but the pulse width of each waveform is different. However, other embodiments of the invention may use other shapes of the waveform.

In a presently preferred embodiment of the invention, the print head is a grayscale head, addressable by a single pulse (i.e., a square wave of nozzle firing times). The single pulse for the nozzle on time is typically 6 to 10 microseconds. For different printheads, the pulse width may exceed this range in different applications, which is merely an example of faster or slower ejection of ink drops from each nozzle. In embodiments of the present invention, the values of the waveform may also be determined by empirically summarizing the experience through trial and error.

However, in the presently preferred embodiment of the invention, waveforms can be created by printing using waveforms and measuring the output to determine ink velocity and drop volume, and to see how the nozzle changes with each different waveform. Thus, the nozzle is characterized to understand how to respond to different waveforms. The waveform may be set in the printer hardware by a software generator for each printhead in each printer, whereby in some embodiments the waveform may be changed at any time. The waveform may be set for each nozzle in each different print head or may be set for each printer to characterize all print heads. The presently preferred embodiment of the present invention looks at the average of all print heads, e.g., the average of each color, corresponding to each other, and then uses the average waveform of each nozzle to drive each nozzle.

In some embodiments of the present invention, a lookup table containing waveforms is created. The presently preferred embodiment of the present invention provides a look-up table having 25 to 30 different waveform sets. Thus, a full set of waveforms may be used for the printhead, e.g., 7 or 8 waveforms may be used at any point in time. In the look-up table, the printer may contain 30 sets of 7 waveforms.

Two adjustments are made in the presently preferred embodiment of the invention: mapping adjustment and waveform set adjustment.

The mapping adjustment may map each nozzle in the printhead to a particular reference point (e.g., a 0 to 73 bit system), where zero is the baseline waveform. Thus, the baseline of the waveform set is zero, with the very fast waveform being 7. Thus, in this embodiment, there are 8 different waveforms from slow to fast or small to large. By varying the increments from top to bottom, one typical mapping for each jet can be used to control the amount of adjustment of the print head. In an embodiment of the invention, the user interface includes a slider that allows the user to increase or decrease the waveform increment between each nozzle.

If the last 25 nozzles of the print head are slow, but not all nozzles are slowed by the same amount, the characteristics at the ends of the print head can be mapped and a 0 to 7 correction can be made for the last 25 nozzles. The middle nozzle, which may be noisier than the difference, may apply the reference waveform to such nozzles.

The mapping is changed in response to characterizing the defect. This characterization can cause the waveform to tilt, thereby eliminating the defect to be corrected. The defect is mapped by analysis, and a feature map of the defect is created. In fact, the defects can be corrected by adjusting the nozzle waveform, which is a necessary measure to eliminate the defects. The adjustments to each waveform may be mapped to the printhead and stored in a look-up table. As described above, in embodiments of the invention, the maps may be created for each printhead individually, but other embodiments of the invention may send the same map to all of the printheads in the printer, e.g., the same map for each individual nozzle may be used in the printer, e.g., each of the 48 printheads.

The second adjustment adjusts the set of waveforms itself. As described above, the exemplary mapping range is 0 to 7, but any other range of values may be selected as desired. The range may process any selected waveform and increase or decrease the amount of adjustment to which the mapping is applicable. In effect, this adjustment scales the mapping.

Some waveforms are wider (i.e., longer duty cycle) than others, which means that there is more energy in the waveform to drive the nozzle. More energy associated with the pulse width does not always result in faster and larger ink deposition. In the preferred embodiment of the present invention, the pulse width is approximately 8 microseconds, but the actual optimum pulse width range may vary depending on print head, ink, etc.; the presently preferred embodiment of the present invention provides pulse widths that can range up to about 8.2 microseconds for a single pulse. If the duty cycle or nozzle opening time is shorter, less energy is required to transfer into the ink drops. The waveform is characterized by an ink drop size and velocity that can be correlated with each waveform for each nozzle to create a defect map.

In an embodiment of the present invention, an exemplary printer (e.g., Vutek HS100) uses a 12 picoliter SeikoGS508 printhead. Embodiments of the present invention may characterize a range of print heads based on defects in the print heads and/or defects associated with the printer mode, for example, the manner in which the print modes are interleaved may also exhibit different defects. As such, in some cases, it is advantageous to characterize different modes.

Thus, the printer may have a library of look-up tables from which the printer may select a particular look-up table, based on logic in the printer that identifies when a user selects a particular mode. In other embodiments, if the printhead manufacturer provides a comprehensive data set for the printhead used in the final test that characterizes each nozzle, such data can be used to automatically create a look-up table. The table may be adjusted according to experience with the printer, if desired.

Embodiments of the present invention also provide different tables for each color ink based on the different characteristics of each ink. For example, different waveform sets or different look-up tables may be provided for clear inks or white inks used in printers that have different characteristics than other inks.

The look-up table embodies a characteristic curve negating the performance attribute; the performance attributes may be analyzed and a curve or look-up table created. It is undesirable to have a large difference between adjacent nozzles. If one nozzle is weak and an adjacent nozzle is strong, then a very different set of waveforms should not be applied to the adjacent nozzle or adjacent nozzle block to avoid noticeable visible differences in printing. To avoid artifacts, the system can dither between the two waveforms so that the system adjusts, for example, 10 nozzles using not only one waveform, but 10 nozzles using the next waveform. Instead, the system can adjust, for example, 3 or 4 nozzles, one more nozzle, another 3 more nozzles, two more nozzles, etc., to achieve better adjustment. Thus, the system can mix the transitions.

In embodiments of the present invention, the dither increment has a limit. As mentioned above, it is undesirable for the step between nozzles to be so large that significant artifacts are created in the resulting print. Embodiments of the present invention may provide a 0.5 microsecond pulse for nozzle on time as the maximum difference, with a typical difference ranging from 0.1 to 0.2 microseconds. The waveform width difference should not exceed, for example, 0.5 microseconds during the transition from one nozzle to the next. This limitation on waveform deviation is also useful to address cross-talk between adjacent nozzles, where one nozzle may affect another. Nozzles with high spray intensity will also affect adjacent nozzles compared to adjacent nozzles. Applying jitter limits may mitigate this crosstalk.

With respect to print defects, a large portion of the print heads (e.g., 90% of the print heads) can emit noise, where the difference in the portion of the print heads is small and defects of a common character do not occur. The portion of the printhead may be driven by a reference waveform. Thus, the nozzles in the middle 90% of the printhead are normally driven using a standard waveform. As described above, to negate the different performance attributes of the printhead tip (e.g., due to the thermal effects described above), the system may increase the drive applied to each nozzle and overdrive the last 5% of the nozzles at each end of the printhead. This flattens the curve by increasing the energy applied to the nozzles via the waveform of each nozzle as the nozzles get farther from the center of the printhead. Typically, only 5% to 10% of the nozzles at the end of the printhead are corrected. In many cases, there is no need to adjust the remaining nozzles, and such nozzles may be driven using a single waveform, depending on the characteristics of the printhead and/or the performance attributes to be negated.

In embodiments of the present invention, a user can creatively adjust the curve to introduce special effects into the print. Thus, this embodiment of the invention does not address the drawbacks, but rather introduces special handling for the printhead. In this manner, a user may obtain a user interface that includes sliders for increasing or decreasing the correction factor. Instead of changing the look-up table, the user adjusts the waveform difference amplitude applied to each nozzle from highest to lowest.

Embodiments of the present invention may also be used to correct individual nozzles, for example, nozzles having specific defects (e.g., inert nozzles). For such nozzles, it is not desirable to replace the print head, as the rest of the print head can function properly. In this case, the individual nozzles may be driven by different waveforms to correct errors, so that the service life of the print head may be extended.

The print head may be characterized by data provided by the print head manufacturer or by empirically generated data, such data may be used to generate a look-up table. Thus, if there is a speed defect, a separate look-up table may be created for each print head using the manufacturer's characteristic speed data provided simultaneously with each print head. A look-up table is then applied to each print head in the printer so that the print head can achieve full perpendicular firing.

Typically, slight differences in the print head occur, for example, a difference of plus or minus 15% in the velocity within the print head. If not corrected, the straight line will not be perfectly straight, but will be wavy, because some nozzles are slower than others. The print head manufacturer may provide the feature shape. In embodiments of the invention, slow nozzles, fast nozzles, and uniform nozzles may be identified. For example, a camera in the printer may look for point location. In this case, the printer may print the test pattern using one print head to print one line of dots. The camera can read and analyze the test pattern. The dot locations obtained by the camera are fed back to the printer to create a look-up table to correct for offset or speed differences.

From this data, an inverse table can be created, which can then be applied to the printhead by varying the waveform supplied to each nozzle in the printhead one by one. Thereby producing a straight line print. This does not necessarily address the temperature deficiencies in the print head described above, but only addresses the deficiencies of single-point positioning. As described above, the present invention addresses temperature deficiencies. By selecting different waveforms for each nozzle in the printhead, the system can manipulate the ink delivery rate.

Computer implementation

FIG. 12 is a block diagram of a computer system that may be used to implement certain features in some embodiments of the invention. The computer system may be a server computer, a client computer, a Personal Computer (PC), a user device, a tablet computer, a handheld computer, a Personal Digital Assistant (PDA), a cellular telephone, an apple cell phone, an apple tablet, a blackberry, a processor, a telephone, a network device, a network router, switch or bridge, a console, a handheld console, a (handheld) gaming device, music player, any portable or handheld device, a wearable device, or any machine capable of executing a set of instructions, sequences of instructions, or other instructions that specify actions to be taken by that machine.

The computing system 1000 may include one or more central processing units ("processors") 1002, memory 1004, input/output devices 1008, e.g., keyboard and pointing devices, touch devices, display devices, storage devices, e.g., disk drives, and communication devices 1006, e.g., network interfaces, connected to the interconnect 1010.

In FIG. 12, an interconnect is an abstraction that represents any one or more separate physical buses, point-to-point connections, or both, connected by appropriate bridges, adapters, or controllers. Thus, an interconnect can include, for example, a system bus, a Peripheral Component Interconnect (PCI) bus or PCI-serial bus, an ultra-transport or Industry Standard Architecture (ISA) bus, a Small Computer System Interface (SCSI) bus, a Universal Serial Bus (USB), an IIC (12C) bus, or an Institute of Electrical and Electronics Engineers (IEEE) standard 1394 bus, also known as a "firewire.

Memory 1004 and storage devices are computer-readable storage media that store instructions that implement at least a portion of the embodiments of the invention. In addition, the data structures and message structures may be stored or transmitted via a data transmission medium (e.g., a signal on a communication link). Various communication links may be used, such as the internet, a local area network, a wide area network, or a point-to-point dial-up connection. Thus, computer-readable media may include computer-readable storage media (e.g., "non-transitory" media) and computer-readable transmission media.

The instructions stored in the memory 1004 may be implemented as software and/or firmware to program the one or more processors to perform the operations described above. In some embodiments, such software or firmware may be initially provided to processing system 1000 by downloading it from a remote system through a computing system (e.g., through communication device 1006).

The embodiments of the invention described herein may be implemented by programmable circuitry (e.g., one or more microprocessors), for example, programmed with software and/or firmware, or entirely in dedicated, hardwired (i.e., non-programmable) circuitry, or in a combination of such. The dedicated hardwired circuitry may be in the form of, for example, one or more ASICs, PLDs, FPGAs, or the like.

The present invention has been described herein with reference to the preferred embodiments, but those skilled in the art will appreciate that other applications may be substituted for those set forth herein without departing from the spirit and scope of the present invention. Accordingly, the invention is limited only by the following claims.

Claims

1. A method for optimizing the uniformity of performance of inkjet nozzles within a printhead containing a plurality of nozzles, comprising:

characterizing one or more performance attributes of the nozzles in the printhead;

generating a waveform set comprising a plurality of waveforms to compensate for differences in the one or more performance attributes in the nozzle, wherein the waveform set comprises a discrete finite waveform set;

using a dithering operation to assign one of the waveforms to each nozzle, the dithering operation further comprising a dithering increment limit to control a width change of each waveform in the set of waveforms to limit a transition from one nozzle to a next nozzle; and

assigning one of the waveforms within the set of waveforms to each of the nozzles to optimize the one or more performance attributes of each of the nozzles relative to each of the other nozzles in the printhead;

wherein each nozzle in the printhead responds substantially uniformly with respect to each other nozzle in the printhead based on the waveform assigned to each nozzle.

2. The method of claim 1, further comprising: using the dithering operation to smooth transitions between the discrete finite waveforms.

3. The method of claim 1, further comprising:

using performance of a predetermined portion of the nozzles of the printhead as a reference; and

adjusting nozzles outside of the predetermined portion of the nozzles of the printhead by assigning a waveform to the external nozzles to adjust the external nozzles to approximate the performance of the nozzles within the predetermined portion of the nozzles of the printhead.

4. The method of claim 1, wherein the performance attribute comprises any one of: drop velocity, drop volume, drop mass, optical density produced by the printhead, gloss, and temperature of the printhead.

5. The method of claim 1, further comprising: the one or more performance attributes are characterized using a printed test pattern that is subsequently imaged and analyzed.

6. A scanning printer in which the consistency of the performance attributes produced by a given color channel is improved by:

a combined average of the performance attributes characterizing all printheads within the printer;

selecting a waveform for each printhead nozzle from a set of waveforms to make the performance attribute more consistent across the printhead nozzles, wherein the set of waveforms comprises a discrete finite set of waveforms;

the same selected waveform is applied to each printhead printing the given color channel.

7. The scanning printer of claim 6, said performance attribute comprising any one of drop velocity, drop volume, drop mass, optical density produced by said color channel, gloss, and temperature of a printhead printing said color channel.

8. A method for optimizing the uniformity of performance of inkjet nozzles within a printhead containing a plurality of nozzles, comprising:

generating a feature lookup table to identify one or more performance attributes in the printhead;

generating a set of waveforms to compensate for differences between the nozzles in the printhead by driving the nozzles according to the lookup table over a full range of values of the performance attribute characterized by the lookup table, wherein the set of waveforms comprises a discrete finite set of waveforms;

using a dithering operation to assign one of the waveforms to each nozzle, the dithering operation further comprising a dithering increment limit to control a width change of each waveform in the set of waveforms to limit a transition from one nozzle to a next nozzle;

wherein each feature value assigned to each nozzle in the lookup table references one waveform in the set of waveforms; and

driving a respective nozzle in the printhead using each of the waveforms in the set of waveforms;

wherein each nozzle responds substantially uniformly relative to each other nozzle in response to the waveform.

9. The method of claim 8, further comprising: dithering is performed between transitions in a look-up table having a step response to produce smooth transitions between adjacent nozzles, wherein a group of nozzles having the same look-up table value is not immediately adjacent to a group of nozzles having different look-up table values.

10. The method of claim 9, further comprising: the variation of the dither patterns between adjacent nozzles is limited to avoid step and cross-talk defects, wherein one lookup table unit is allowed to go up and down.

11. The method of claim 8, further comprising: setting a portion of the lookup table to a reference waveform value to create a continuous response of adjacent nozzles within a predetermined portion of the printhead.

12. The method of claim 8, further comprising: and generating the lookup table according to the temperature-related data.

13. The method of claim 8, further comprising: and generating the lookup table according to the point position error related data.

14. The method of claim 8, further comprising: and generating the lookup table according to the data related to the droplet speed.

15. The method of claim 8, further comprising: user adjustments are provided for each waveform.

16. The method of claim 8, further comprising: the feature look-up table is empirically generated from scanned or captured and analyzed printed test patterns.

17. The method of claim 8, further comprising: providing a user interface, wherein a look-up table represents a manually adjusted characteristic curve to compensate for differences between the nozzles in the printhead, wherein the manual adjustment selects a different set of waveforms to apply to the performance attribute.